6" to 8" Conversion at the seacow

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Re: 6" to 8" Conversion at the seacow

Postby DrewInToledo » Thu Oct 16, 2014 1:51 pm

Looks great Manny. I agree -- I couldn't see myself purchasing a stove without a window. I can sit and stare into a fire for hours.

Does that remote control on your bench control your RMH? :lol:
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Re: 6" to 8" Conversion at the seacow

Postby mannytheseacow » Thu Oct 16, 2014 2:29 pm

Ha, good catch on the remote, Drew. It doesn't do much for the RMH but we've been having fun pointing it into the pickups on an electric guitar and making robot noises. So much fun, in fact, that I have to get up to push play when I want to watch my old snowboarding videos because the batteries went dead. It's one of those stupid remotes that takes the round watch style batteries... time for the landfill.
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Re: 6" to 8" Conversion at the seacow

Postby mannytheseacow » Sat Oct 18, 2014 7:35 pm

ByronC wrote:
First thing that came to mind, is there anyway to take the 6" (CSA=30 sq. in.) top section off the 7.5" x 7.5" (CSA=56 sq. in.) chimney for a quick test?


Good idea, Byron! I needed some double wall pipe to vent my cookstove, which has higher exhaust temperatures. So I pulled the 6" double wall section off the top of the chimney that vents the rmh and replaced it with 8" single wall. It didn't affect the draw at all, though.
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Re: 6" to 8" Conversion at the seacow

Postby ByronC » Tue Oct 21, 2014 11:46 am

Interesting, and makes one wonder if there may be a bit of a restriction somewhere in the system.

From what I've gathered to date with a by "the book" RMH build, the common trouble spots of stalling hot gases are at the riser top to barrel gap, riser sides to barrel gap, and the manifold area. The consensuses among experienced RMH builders is that the clearances given in the book are minimums, and have a tendency to be a little on the tight side at that.

For my indoor 8" system I'll be setting the top riser to barrel gap at 3". And to gain more riser sides to barrel (55 gal.) clearance, I'm leaning towards making the riser from firebrick splits with a 1" ceramic wool wrap -or- maybe just build the riser from the light insulating kiln brick and leaving off the ceramic wool. Not sure how the latter would hold up over the long haul and have yet to find an example where someone has tried it with insulating kiln brick.
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Re: 6" to 8" Conversion at the seacow

Postby matt walker » Tue Oct 21, 2014 4:38 pm

I think Manny's theory on the fuel is the right angle. I'm pretty sure he's been all through that thing and it flows freely everywhere, but two hours on a load? Yeah, that's a whole different issue and I can for sure see creep happening if it takes that long for the bottoms to burn out and the fuel to drop. How's the draw with the new window Manny? Better? Worse? No change, but looks awesome is what I would guess.

I've got a huge stack of IFB in my shop Byron, let me know if there's anything specific you want to know. It should make a good riser, but it will be a pretty big outside diameter since they run thick in all dimensions.
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Re: 6" to 8" Conversion at the seacow

Postby mannytheseacow » Tue Oct 21, 2014 9:17 pm

Good thoughts, Byron. Those are things that I have looked at, too. With this rebuild I have a huge top-gap so I'm fairly certain it's not that. I think the riser is diameter is about the same as my 6" was, as my 6" had a huge insulative mass around it. The plenum is way bigger... not that much that could go wrong. The only area that could be pinching, in my opinion, is the 180 at the far end. I fabricated 8" ducts into the old 6" cleanouts by cutting the 6" cleanouts with a grinder and splaying them out. wider, covering the area with a sheet of tin over the top, and cobbing around it. I'm pretty sure it's ok, but I've never really measured it. One thing that I did try was connecting two 6" 90s to the cleanouts there to make a loop that redirected flow back around and increasing the volume in that area.... and it had no effect.

I'm with Matt on the fuel. I've worked through some large crotch splits at the front of my pile and gotten into some older, dryer, smaller fuel and there are no smoke-back issues. These loads tend to burn through in 30-40 minutes.

Matt, the window is pretty cool, and mostly aesthetic. Honestly, it hasn't really had any effect on draw, though I love being able to load longer fuel and leave it without trying to balance the inverted pot on the top of a stick, hoping it falls correctly as the fuel burns down. The one downside to my window is that it is up a little higher on the stove. The bottom of the window stays clean but the top and edge farthest from the burn tunnel have gotten pretty black from smoke. It still lets light through but not as much as if it were viewing the burn tunnel.

Actually, I hate it. It works real good and now I have no reason to be tinkering with the stove. Bah!
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Re: 6" to 8" Conversion at the seacow

Postby ByronC » Fri Oct 24, 2014 11:20 am

Excellent Manny. As for me, I like a stove where the only tinkering has to do with feeding it fuel, especially in the middle of a polar vortex wobble:->

Matt, sounds like you've been working a bit with IFB? In re. to making a square insulated riser from IFB, I am thinking of the fat husky IFB which you mentioned. I.e. the ones that measure 3.0 x 4.5 x 9.0 inches. Each IFB would be sliced into two equal bricks of 1.5 x 4.5 x 9.0, and stacked on edge to make the heat riser with a wall thickness of 1.5".

Do you feel that such an IFB riser would be insulating enough compared to a riser made from 1" ceramic wool rapped dense firebrick (1.25" thick) splits? Do IFB play well with clay slip mortar or is there something better?
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Re: 6" to 8" Conversion at the seacow

Postby matt walker » Fri Oct 24, 2014 5:40 pm

They work well with clay mortar, but one of the interesting things I learned in Montana is that clay slip isn't enough. You should add some sand and make a real mortar or you will get gaps, in any brick work. Slip is only good for temporary set ups.

I think heavy bricks, even splits, are detrimental to the system anywhere in the combustion zone, so I think split IFB is better for sure. That's an opinion, but, yeah. The workshop I taught in NH a few weeks ago we used ceramic fiber board and just build square risers with that. They went together super quick and didn't use a whole lot of material. I liked that technique. If you have the IFB, your plan sounds good, but man, those things are fragile. I think splitting them is going to make them more so. I think I'd choose a simple method myself, but then again, if you have 'em, run 'em.
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Re: 6" to 8" Conversion at the seacow

Postby ByronC » Fri Oct 24, 2014 10:21 pm

Matt, about the IFB for making a riser, I'm not locked into that nor have I bought any IFB yet. Just toying with several ideas here with the aim of building the ultimate J-tube RMH. Ultimate as in striking a balance between optimum operating performance together with a long lived maintenance free core and riser. A while back I was looking into Fiberfrax Duraboard, and thinking about using it to make easily replaceable J-tube firebox lining components, slid in through a front door to the burn tunnel. Then sticker shock set in when I began pricing the Fiberfrax.

For the square risers you're making, now that's a great idea using the ceramic fiber board. What thickness material and how are you holding the pieces together? A good place to source the material from?
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Re: 6" to 8" Conversion at the seacow

Postby matt walker » Fri Oct 24, 2014 10:29 pm

I think the ultimate is the formed risers I'm using, frankly. They aren't too expensive, and are 2"+ wall thickness, and round. That's what we used for Peter's 8" in Montana, and I've been running the 6" ones here for a couple years now. They are great. Same material as the board, just round and thick.

Duraboard risers are a good compromise, but the downside is that I expect they are changing shape during the burn cycle and I'm sure there are leaks. Personally, I don't think it's a show stopper, but I do think the solid round ones are better. Anyway, you can pin them together with stainless drywall type screws. I don't think it's worth giving you a source, as the best source is the one closest to you. Any major industrial refractory house will have it, in various thicknesses. I've had good luck with 1" board, but the thicker the better. Duraboard is just Fiberfrax's brand name for the ceramic fiber board.
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